The present invention relates to an apparatus for preventing inadvertent admixture of friction-reducing additives to water in transient flow conditions, such as, for example, during starting and shutdown. The apparatus has a reservoir for the additives, and is connected, by means of a supply line, with a mixing nozzle for admixing the additives to the water.
German Laid Open Patent Application (Offenlegungsschrift) No. 2,051,873 discloses a method and apparatus for mixing soluble polymer materials with a liquid and teaches, in particular, the easy and effective mixing of soluble materials with a liquid solvent. With this method and apparatus flow resistance-reducing solutions can be produced in a continuous manner.
The method and apparatus disclosed in the cited Offenlegungsschrift serve to mix an additive with a liquid in order to inject this mixture into a boundary layer for the reduction of friction between the liquid and the surface of a body moving relative to the liquid. In particular, it is possible to utilize the method and the apparatus in navigation for the quick admixture of a polymer additive to water. The polymer is effectively hydrated immediately prior to its injection along the surface where friction is to be reduced.
In the cited Offenlegungsschrift an apparatus is described for admixing friction-reducing additive. The apparatus includes a mixing chamber for rapidly forming a suspension of the soluble polymer material in a solvent, a vessel for hydrating the suspension and an apparatus for injecting the resulting solution into the boundary layer with a flow speed sufficient for a reduction in friction. The suspension is hydrated in this case until a substantial solution of the polymer has been formed; the solution has a stronger concentration than required for the reduction of friction. The mixing chamber may include an arrangement in which the polymer material is brought into contact with a jet stream of solvent and which the hydration continues during the passage of the solution. Means may also be provided for thinning the solution with added solvent. This apparatus has the drawback that during transient flow conditions, such as during starting and shutdown, clogging may occur in the polymer supply lines, because during these flow phases it is possible for the polymer suspension to change its direction of movement. This immediately has the result that the individual polymer molecules of the suspension form with water either lumps in high concentrations, or a very viscous immovable solution. It has been found in practice that restarting is then impossible and the mixing assembly forming the mixing circuit must be disassembled.